Added callback to DownloadUrl() so we can find download failures.

content/public/browser/download_manager.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // The DownloadManager object manages the process of downloading, including
 // updates to the history system and providing the information for displaying
 // the downloads view in the Destinations tab. There is one DownloadManager per
 // active browser context in Chrome.
 //
 // Download observers:
@@ skipping 44 matching lines @@
 namespace content {
 class BrowserContext;
 class DownloadManagerDelegate;
 class DownloadQuery;
 class WebContents;
 
 // Browser's download manager: manages all downloads and destination view.
 class CONTENT_EXPORT DownloadManager
     : public base::RefCountedThreadSafe<DownloadManager> {
  public:
+  typedef base::Callback<void(DownloadId, net::Error)> OnStartedCallback;
+
   virtual ~DownloadManager() {}
 
   static DownloadManager* Create(
       DownloadManagerDelegate* delegate,
       net::NetLog* net_log);
 
   // Shutdown the download manager. Must be called before destruction.
   virtual void Shutdown() = 0;
 
   // Interface to implement for observers that wish to be informed of changes
@@ skipping 94 matching lines @@
   // Downloads the content at |url|. |referrer| and |referrer_encoding| are the
   // referrer for the download, and may be empty. If |prefer_cache| is true,
   // then if the response to |url| is in the HTTP cache it will be used without
   // revalidation. If |post_id| is non-negative, then it identifies the post
   // transaction used to originally retrieve the |url| resource - it also
   // requires |prefer_cache| to be |true| since re-post'ing is not done.
   // |save_info| specifies where the downloaded file should be
   // saved, and whether the user should be prompted about the download.
   // |web_contents| is the web page that the download is done in context of,
   // and must be non-NULL.
+  // |callback| will be called when the download starts, or if an error
+  // occurs.

[Randy Smith (Not in Mondays), 2012/03/06 21:29:14]

You should specify the calling interface to callback.  I think the only part
that isn't obvious from the signature is that DownloadId will be invalid? 
unspecified?  If net::Error is not net::OK.

(This could also be done at the typedef; that's probably a better location for
it, actually.)

[ahendrickson, 2012/03/06 22:01:36]

Heh, I added that information to the typedef in the last CL.

   virtual void DownloadUrl(const GURL& url,
                            const GURL& referrer,
                            const std::string& referrer_encoding,
                            bool prefer_cache,
                            int64 post_id,
                            const DownloadSaveInfo& save_info,
-                           content::WebContents* web_contents) = 0;
+                           content::WebContents* web_contents,
+                           const OnStartedCallback& callback) = 0;
 
   // Allow objects to observe the download creation process.
   virtual void AddObserver(Observer* observer) = 0;
 
   // Remove a download observer from ourself.
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Called by the embedder, after creating the download manager, to let it know
   // about downloads from previous runs of the browser.
   virtual void OnPersistentStoreQueryComplete(
@@ skipping 84 matching lines @@
   friend class base::RefCountedThreadSafe<
       DownloadManager, content::BrowserThread::DeleteOnUIThread>;
   friend struct content::BrowserThread::DeleteOnThread<
       content::BrowserThread::UI>;
   friend class base::DeleteHelper<DownloadManager>;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_H_